Adhesive sheet of cross-linked silicone, method of manufacturing thereof, and device

ABSTRACT

A cross-linked silicone adhesive sheet has stability of peeling surfaces during peeling protective films away from both sides of the sheet. An adhesive sheet of a cross-linked silicone has protective films on both sides of the sheet. The protective films each have a thickness of 100 μm or less. A force of peeling of the protective films from the sheet is equal to or below 5.0 N/m. The difference between peeling forces of the films is equal to or exceeds 0.2 N/m. A method of manufacturing the adhesive sheet of a cross-linked silicone includes the steps of forming a film-like body by placing a cross-linkable silicone composition in a layer having a thickness of 100 μm or less between two protective films of different materials and then cross-linking the composition.

[0001] The present invention relates to cross-linked silicone adhesivesheets and to a method of manufacturing such sheets, more particularly,to cross-linked silicone adhesive sheets having surfaces of high peelingstability, as well as to an effective method of manufacturing sheets ofthe aforementioned type.

BACKGROUND

[0002] Japanese Laid-Open Patent Application Publication H11- 12546, andits equivalent, U.S. Pat. No. 6,235,862, discloses a silicone adhesivesheet with protective films adhered to both sides of the sheet. Theaforementioned sheet is intended for use as an adhesive means forattachment of semiconductor chips or chip supports. The protective filmson both side of the aforementioned adhesive sheet are normally made fromthe same material.

[0003] However, if a cross-linked silicone adhesive sheet is made as athin film with a thickness of 100 micrometers (μm) or less, conditionsof peeling of the protective film from either side of the sheet becomeunstable.

[0004] It is an object of the present invention to provide an adhesivesheet of a cross-linked silicone characterized by stability of peelingof protective films from both sides of the sheet, as well as to providean efficient method of manufacturing of the aforementioned adhesivesheet.

THE INVENTION

[0005] The invention relates to an adhesive sheet of a cross-linkedsilicone with a thickness of 100 μm or less, and protective filmsadhered on both sides of said sheet, wherein a force of peeling of theprotective films from the aforementioned sheet is equal to or below 5.0Newtons per meter (N/m) and wherein the difference between peelingforces of the films is equal to or exceeds 0.2 N/m.

[0006] A method of the present invention for manufacturing an adhesivesheet of a cross-linked silicone comprises forming a film-like body byplacing a cross-linkable silicone composition in a layer having athickness of 100 μm or less between two protective films and thencross-linking the composition. The method is characterized by making theprotective films from different materials.

[0007] According to another aspect of the invention, a method ofmanufacturing an adhesive sheet of a cross-linked silicone by forming afilm-like body by placing a cross-linkable silicone composition in alayer having a thickness of 100 μm or less between two protective filmsand then cross-linking the composition, is characterized by the factthat the composition side of one of the protective films adhered to thecomposition is pretreated with an organopolysiloxane having at least twosilicon-bonded hydrogen atoms in one molecule.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a cross-sectional view of hybrid integrated circuit (IC)as an example of a semiconductor device that can be produced with theuse of the cross-linked silicone adhesive sheet of the invention.

REFERENCE NUMERALS USED IN THE DESCRIPTION

[0009]1 semiconductor chip

[0010]2 cross-linked silicone adhesive sheet

[0011]3 semiconductor chip support member

[0012]4 interconnects

[0013]5 bonding wires

[0014]6 sealing resin

DETAILED DESCRIPTION OF THE INVENTION

[0015] A cross-linked silicone adhesive sheet of the present inventionwill now be described in more detail. As mentioned above, an adhesivesheet of the present invention is made from a cross-linked silicone witha thickness of 100 μm of less between protective films adhesivelyattached to both sides of the sheet. The aforementioned cross-linkedsilicone may comprise an elastomer in the form of a rubber or gel, butthe rubber form is preferable. Furthermore, the cross-linked siliconeadhesive sheet can be produced by cross-linking a cross-linkablesilicone composition. Examples of the cross-linkable siliconecomposition suitable for the invention are those that can becross-linked by a hydrosilylation reaction, a condensation reaction, aradical cross-linking reaction with the use of an organic peroxide, orwith the use of ultraviolet rays, but the one that is cross-linked by ahydrosilylation reaction is preferred.

[0016] A silicone composition cross-linkable by a hydrosilylationreaction may comprise at least the following components: (A) anorganopolysiloxane having at least two alkenyl groups in one molecule;(B) an organopolysiloxane having at least two silicon-bonded hydrogenatoms in one molecule; (C) adhesion accelerator; and (D) a metalhydrosilylation catalyst.

[0017] An organopolysiloxane of component (A) is a main component of theaforementioned composition and is characterized by having at least twoalkenyl groups in one molecule. Examples of the molecular structures ofcomponent (A) include linear, linear with some branches, branched, andnet-like structures. Examples of the alkenyl groups in component (A)include vinyl, allyl, butenyl, pentenyl, and hexenyl, with the vinylgroup being preferred. The bonding positions of these alkenyl groups incomponent (A) may be at the molecular chain terminals and/or pendant.Examples of silicon-atom-bonded groups, other than alkenyl groups incomponent (A), include substituted and unsubstituted monovalenthydrocarbon groups such as the methyl, ethyl, propyl, butyl, pentyl,hexyl, heptyl, and other alkyl groups; aryl groups such as phenyl,tolyl, xylyl, and naphthyl; aralkyl groups such as benzyl and phenethyl;and halogenated alkyl groups such as chloromethyl, 3-chloropropyl, and3,3,3-trifluoropropyl. The methyl groups and phenyl groups arepreferred. To improve resistance of the cross-linked silicone sheet tocold and thus to improve reliability of a semiconductor device obtainedby attaching a semiconductor chip or a chip-supporting member to theaforementioned sheet, it is recommended that for the phenyl group thecontent be at least 1 mol %, with a range of 1 to 60 mol % beingpreferred, and a range of 1 to 30 mol % being more preferred, withrespect to the organic groups bonded to silicon atoms in component (A).There are no restrictions on the viscosity of component (A), but a rangeof 100 to 1,000,000 milli-Pascal seconds (mPa.s) at 25° C. ispreferable.

[0018] An organopolysiloxane of component (B) is a cross-linking agentand is an organopolysiloxane having at least two hydrogen atoms bondedto silicon atoms per molecule. Examples of the molecular structure ofcomponent (B) include linear, linear with some branches, branched, andnet-like. The bonding positions of the hydrogen atoms to silicone atomin component (B) may be at the molecular chain terminals and/or pendant.Examples of silicon atom-bonded groups other than hydrogen atoms incomponent (B) include substituted and unsubstituted monovalenthydrocarbon groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl,heptyl, and other alkyl groups; aryl groups such as phenyl, tolyl,xylyl, and naphthyl; aralkyl groups such as benzyl and phenethyl, andhalogenated alkyl groups such as chloromethyl, 3-chloropropyl, and3,3,3-trifluoropropyl. The methyl group and phenyl group areparticularly favorable. There are no restrictions on the viscosity ofcomponent (B), but a range of 1 to 100,000 mPa•s at 25° C. ispreferable.

[0019] Although there are no special restrictions on the amount ofcomponent (B) required for use in the composition, it is recommendedthat this component be contained in an amount sufficient forcross-linking of the above composition. More specifically, it should beused in an amount from 0.5 to 10 moles, preferably between 1 and 3 molesof silicon-bonded hydrogen atoms per mole of alkenyl groups in component(A). This is because cross-linking will tend to be inadequate ifcomponent (B) is used in an amount less than the recommended range, butif the amount of component (B) used exceeds the recommended upper limit,the heat resistance of the cross-linked adhesive sheet obtained willtend to be lower.

[0020] Component (C) is an agent that increases the adhesiveness of thecomposition and is used to impart particularly good adhesiveness to thecross-linked silicone product of the above composition. An organicsilicon compound having at least one silicon-bonded alkoxy group permolecule is preferable for use as compound (C). The aforementionedalkoxy group can be represented by a methoxy, ethoxy, propoxy, butoxy,and methoxyethoxy group, the most preferable of which is a methoxygroup. The following are examples of groups other than the alkoxy groupsbonded to silicon atoms in the aforementioned organic silicon compounds:hydrogen atoms; substituted and unsubstituted monovalent hydrocarbongroups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, andother alkyl groups; vinyl, allyl, butenyl, pentenyl, hexenyl, and otheralkenyl groups; phenyl, tolyl, xylyl, naphthyl, and other aryl groups;benzyl, phenethyl, and other aralkyl groups; chloromethyl,3-chloropropyl, 3,3,3-trifluoropropyl, and other halogenated alkylgroups; 3-glycidoxypropyl, 4-glycidoxybutyl groups, and otherglycidoxyalkyl groups; 2-(3,4-epoxycyclohexyl)ethyl,3-(3,4-epoxycyclohexyl)propyl, and other epoxycyclohexylalkyl groups;monovalent organic groups that contain epoxy groups such as4-oxyranylbutyl, 8-oxyranyloctyl, and other oxyranylalkyl groups;monovalent organic groups that contain acryl groups such as3-methacryloxypropyl groups, or the like. It is recommended that theaforementioned organic silicon compounds contain in one molecule atleast one alkenyl group or a silicon-bonded hydrogen atom. Furthermore,from the point of view of improved adhesion of substrates of variousmaterials to the adhesive silicone sheets produced by cross-linking theaforementioned composition, it is recommended that the aforementionedorganic silicone compound contain in one molecule a monovalent organicgroup with at least one epoxy group. Such organic silicon compounds canbe represented by silanes, siloxanes, and silatranes. The aforementionedsiloxane compounds may have a linear, linear with some branches,branched, cyclic, and net-like structure. The linear, branched, andnet-like structures are preferable. The following are specific examplesof the aforementioned organic silicon compounds: 3-glycidoxypropyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyl trimethoxysilane,3-methacryloxypropyl trimethoxysilane, or a similar silane compound; asiloxane compound having in one molecule at least one of the following:a silicon-bonded alkenyl group, a silicon-bonded hydrogen atom, or asilicon-bonded alkoxy group; a mixture of a silane or a siloxanecompound having at least one silicon-bonded alkoxy group with a siloxanecompound having in one molecule at least one of the following: asilicon-bonded hydroxy group or a silicon-bonded alkenyl group; asiloxane compound expressed by the following general formula:

[0021] where a, b, and c are positive numbers;

[0022] a siloxane compound expressed by the following general formula:

[0023] a silatrane compound expressed by the following general formula:

[0024] or a silatrane compound expressed by the following generalformula:

[0025] Although there are no special restrictions with regard to theamount of component (C) suitable for use in the composition of theinvention, it should be sufficient for providing good adhesion to thecross-linked silicone adhesive sheet produced by cross-linking theaforementioned composition. More specifically, it is recommended to usecomponent (C) in an amount of 0.01 to 20, preferably 0.1 to 10 parts byweight for each 100 parts by weight of component (A). This is because,if the aforementioned amount is below the lower recommended limit, theadhesive sheet will have a tendency to decrease in adhesivity, and ifthe aforementioned amount exceeds the upper recommended limit, thenalong with the decrease in adhesivity, the cross-linked siliconeadhesive sheet will have a tendency of variation in mechanicalproperties.

[0026] Component (D) is a metal catalyst that accelerates thehydrosilylation reaction-based cure of the composition. Component (D)can be, e.g., platinum catalysts, rhodium catalysts, and palladiumcatalysts. To provide better cross-linking reaction rates, it isrecommended to use platinum catalysts. The platinum catalysts can beexemplified by platinum micro powder, platinum black, platinum supportedon silica micro powder, platinum supported on active carbon,chloroplatinic acid, alcohol solutions of chloroplatinic acid, olefincomplexes of platinum, and alkenylsiloxane complexes of platinum.

[0027] Although there are no special restrictions with regard to thequantity in which component (D) should be used, it is recommended to addit in sufficient quantity to accelerate the cure of the compositionunder consideration. When a metal catalyst is used as component (D), thecatalyst will be added so as to provide the subject composition withpreferably from 0.01 to 1,000 weight-ppm metal based on the weight ofthe composition and particularly preferably from 0.1 to 500 weight-ppmmetal based on the weight of the composition. The rate of cross-linkingdeclines substantially when the addition of component (D) falls belowthe given range. Additions above the given range have little effect onthe cure rate, but cause such problems as, for example, discoloration.

[0028] For adjusting the rate of cross-linking, the composition of theinvention can be combined with a hydrosilylation reaction inhibitor,such as 3-methyl-1-butyn-3-ol, 3,5-dimethyl-1-hexyn-3-ol, andphenylbutynol; ene-yne compounds such as 3-methyl-3-penten-1-yne and3,5-dimethyl-3-hexen-1-yne; and also1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane,1,3,5,7-tetramethyl-1,3,5,7-tetrahexenylcyclotetrasiloxane, andbenzotriazole. Although there are no special restrictions for theamounts in which the above inhibitors can be used, it is recommended toadd these inhibitors in the range from 0.00001 to 5 parts by weight foreach 100 parts by weight of component (A).

[0029] Other components that may be added on an optional basis to thecurable silicone composition under consideration are exemplified byinorganic fillers such as precipitated silica, wet-process silica, fumedsilica, calcined silica, titanium oxide, alumina, glass, quartz,aluminosilicates, iron oxide, zinc oxide, calcium carbonate, carbonblack, silicon carbide, silicon nitride, boron nitride, and so forth;these inorganic fillers after treatment with an organosilicon compoundsuch as an organohalosilane, organoalkoxysilane, or organosilazane;organic resin micro powders, such as those of silicone resins, epoxyresins, and fluororesins; particulate fillers of electrically conductivemetals such as silver and copper; and also dyes, pigments, flameretardants, and solvents.

[0030] The cross-linked silicone adhesive sheet of the present inventionhas protective films adhered to both sides of the sheet. Such protectivefilms protect adhesive surfaces of the sheet from contamination by dirtand must be peeled away from the adhesive sheet prior to use of theadhesive sheet. It is required that a force of peeling of the protectivefilms from both sides of the cross-linked silicone adhesive sheet of thepresent invention be equal to or below 5.0 N/m. If a force required forpeeling a protective film from the cross-linked silicone adhesive sheetexceeds 5.0 N/m, there is a chance that the protective film will bebroken. Another requirement is that the difference between peelingforces on both sides of the adhesive sheet be 0.2 N/m or greater,preferably 0.5 N/m or greater. If the aforementioned difference is belowthe indicated limit, it would be difficult to provide stability ofpeeling over the entire peeling surface.

[0031] The protective films can be made from a polyethersulfone resin(PES), acetyl cellulose resin, polyimide resin, polyester resin,polyether resin, epoxy resin, phenol resin, polyamide resin, or asimilar organic resin; be made by coating the aforementioned resins on asurface of films made from other organic resins, or be made bylaminating the aforementioned resins and the other organic resins. Theaforementioned acetyl cellulose resin can be exemplified by diacetylcellulose resin and triacetyl cellulose resin (TAC). The difference inpeeling forces on both sides of the sheet can be increased by makingprotective films adhered to both sides of the sheet from differentmaterials. A combination of the protective films can be, e.g., acombination of PES film and acetyl cellulose resin film, a combinationof PES film and the other organic resins film with acetyl celluloseresin layer on the surface, a combination of the other organic resinsfilm with PES layer on the surface and acetyl cellulose resin film, anda combination of the other organic resins film with PES layer on thesurface and the other organic resins film with acetyl cellulose resinlayer on the surface. It is recommended to use a combination of PES filmand acetyl cellulose resin film, a combination of PES film andpolyethyleneterephthalate (PET) film with acetyl cellulose resin layeron the surface, or a combination of PET film with PES layer on thesurface and PET film with acetyl cellulose resin layer on the surface.On the other hand, the difference in peeling forces on both sides of thesheet also can be increased by pre-treating a surface of either one ofthe protective films, to which said composition is applied, with anorganopolysiloxane having at least two silicon-bonded hydrogen atoms inone molecule. The organopolysiloxane having at least two silicon-bondedhydrogen atoms in one molecule and used for pretreatment of theprotective film may be the same as the organopolysiloxane of component(B). Where one protective film has a surface pretreated with theorganopolysiloxane having at least two silicon-bonded hydrogen atoms permolecule, the protective films may be made from the same or differentmaterials. Where neither protective film has a surface pretreated withan organopolysiloxane having at least two silicon-bonded hydrogen atomsper molecule, the protective films are made from different materials.

[0032] A method of manufacturing a cross-linked silicone adhesive sheetof the invention comprises sandwiching a cross-linkable siliconecomposition between two protective films, so that the thickness of thelayer of the composition does not exceed 100 μm, and then forming across-linked silicone adhesive sheet by cross-linking the composition,the protective films being made from different materials.

[0033] Examples of cross-linked silicone compositions suitable for usein the method of the invention are the following: a silicone compositioncross-linkable via a hydrosilylation reaction, a silicone compositioncross-linkable via a condensation reaction, a silicone compositioncross-linkable via a radical reaction with the use of an organicperoxide, and a silicone composition cross-linkable under the effect ofhigh-energy radiation. The most preferable is a silicone compositioncross-linkable via a hydrosilylation reaction. It is recommended thatthe aforementioned silicone composition cross-linkable in ahydrosilylation reaction comprise at least the following components: (A)an organopolysiloxane having at least two alkenyl groups in onemolecule; (B) an organopolysiloxane having at least two silicon-bondedhydrogen atoms per molecule; (C) adhesion accelerator; and (D) a metalhydrosilylation catalyst. The silicone composition cross-linkable via ahydrosilylation reaction and used in the present invention is the onedescribed earlier.

[0034] The protective films suitable for use in the method of theinvention can be made from a polyethersulfone resin (PES), acetylcellulose resin, polyimide resin, polyester resin, polyether resin,epoxy resin, phenol resin, polyamide resin, or a similar organic resin;be made by coating the aforementioned resins on a surface of films madefrom other organic resins, or be made by laminating the aforementionedresins and the other organic resins. The aforementioned acetyl celluloseresin can be exemplified by diacetyl cellulose resin and triacetylcellulose resin (TAC). In the method of the invention, thecross-linkable silicone composition is sandwiched between two protectivefilms which may be made of different materials. Although there are notspecial restrictions with regard to a combination of the protectivefilms for use on opposite sides of the sheet, the combination ofprotective films can be, e.g., a combination of PES film and acetylcellulose resin film, a combination of PES film and the other organicresins film with acetyl cellulose resin layer on the surface, acombination of the other organic resins film with PES layer on thesurface and acetyl cellulose resin film, and a combination of the otherorganic resins film with PES layer on the surface and the other organicresins film with acetyl cellulose resin layer on the surface. It isrecommended to use a combination of PES film and acetyl cellulose resinfilm, a combination of PES film and polyethyleneterephthalate (PET) filmwith acetyl cellulose resin layer on the surface, or a combination ofPET film with PES layer on the surface and PET film with acetylcellulose resin layer on the surface.

[0035] In the method of the invention, a film-like product is formed bysandwiching a cross-linkable silicone composition between two protectivefilms, and then a cross-linkable silicone adhesive sheet is formed bycross-linking the aforementioned composition. Cross-linking can becarried out by retention at room temperature, at 200° C. or less,preferably 120° C. or less, or by irradiating with an electron beam.

[0036] According to another method of the invention, a film-like productis forned by sandwiching a cross-linkable silicone composition betweentwo protective films so that the thickness of the composition layerbecomes 100 μm or less, and a cross-linked silicone adhesive sheet isformed by cross-linking the aforementioned composition. In this case thesurface of a protective film adhered to one side of the composition ispretreated with an organopolysiloxane having at least two silicon-bondedhydrogen atoms per molecule.

[0037] The cross-linkable silicone compositions suitable for the methodof the invention are those that can be cross-linked by a hydrosilylationreaction, a condensation reaction, a radical cross-linking reaction withthe use of an organic peroxide, or with the use of ultraviolet rays, butthe one that is cross-linked by a hydrosilylation reaction is preferred.It is preferable that the silicone composition cross-linkable by ahydrosilylation reaction comprise at least the following components: (A)an organopolysiloxane having at least two alkenyl groups in onemolecule; (B) an organopolysiloxane having at least two silicon-bondedhydrogen atoms in one molecule; (C) adhesion accelerator; and (D) ametal hydrosilylation catalyst. For the reasons described earlier, theuse of the silicone composition cross-linkable by a hydrosilylationreaction is preferable.

[0038] The protective films suitable for the method of the invention maybe represented by a polyethersulfone resin (PES), acetyl celluloseresin, polyimide resin, polyester resin, polyether resin, epoxy resin,phenol resin, polyamide resin, or a similar organic resin; be made bycoating the aforementioned resins on a surface of films made from otherorganic resins, or be made by laminating the aforementioned resins andthe other organic resins. The aforementioned acetyl cellulose resin canbe exemplified by diacetyl cellulose resin and triacetyl cellulose resin(TAC). In the method of the invention, the protective films, betweenwhich the cross-linkable silicone composition is sandwiched, can be madefrom different as well as from the same materials. It is required thatthe composition side of either of the protective films adhered on thecomposition be pretreated with an organopolysiloxane having at least twosilicon-bonded hydrogen atoms in one molecule. Such organopolysiloxanemay be the same as aforementioned component (B). The aforementionedorganopolysiloxane having at least two silicon-bonded hydrogen atoms inone molecule can be applied onto the surface of the protective film bysimple spreading with subsequent heat treatment.

[0039] Thus the method of the invention is carried out by placing across-linkable silicone composition between two films to form afilm-like product and then cross-linking the composition to produce across-linked silicone adhesive sheet. Cross-linking of thecross-linkable silicone composition can be performed by retaining thecomposition at room temperature, at 200° C. or less, preferably 120° C.or less, or by irradiating with an electron beam.

[0040] The cross-linked silicone adhesive sheet of the invention is usedfor attaching a semiconductor chip to a chip support. It is recommendedthat the cross-linked silicone adhesive sheet contain a minute quantityof uranium or thorium, e.g., with the total amount of no more than 1ppb. The cross-linked silicone adhesive sheet may contain a small amountof ions of sodium, potassium, or of a similar alkali metal, inparticular, in an amount of no more than 1 ppm.

[0041] A method of manufacturing a semiconductor device with the use ofthe aforementioned cross-linked silicone adhesive sheet will now bedescribed in more detail. Applicable semiconductor devices can beexemplified by diodes, transistors, thyristors, monolithic integratedcircuits, hybrid integrated circuits, large-scale integrated circuits,and very large-scale integrated circuits. An examples of semiconductordevice according to the present invention is shown in FIG. 1, which is across section of a hybrid integrated circuit. In the semiconductordevice shown in FIG. 1, a semiconductor chip 1 is bonded to asemiconductor chip support 3 using a cross-linked silicone adhesivesheet 2. The semiconductor chip 1 and interconnects 4, which areconnected to the outer leads, are electrically connected to thesemiconductor chip 1 by bonding wires 5. The semiconductor chip 1 maycomprise a memory unit of a diode, transistor, thyristor, monolithicintegrated circuit, or of a hybrid integrated circuit, or asemiconductor chip in a hybrid integrated circuit. The semiconductorchip support 3 can be made from a ceramic, glass, epoxy resin, polyimideresin, phenolic resin, bakelite resin, melamine resin, glassfiber-reinforced epoxy resin, and glass fiber reinforced BT resin. Theinterconnects 4 can be made of gold, copper, aluminum, silver-palladium,indium-tin oxide (ITO), and so forth. The bonding wires 5 can be made ofgold, copper, or aluminum. The semiconductor element 1 is also sealedwith a sealant resin 6. The resin making up the sealant resin 6 can beexemplified by epoxy resin, phenolic resin, and polyphenylene sulfideresin. In addition to the semiconductor chip 1, other electroniccomponents, e.g., resistors, capacitors, coils, etc., can be mounted onthe circuit substrate 3.

[0042] The method for attaching the semiconductor chip to theaforementioned chip support via a cross-linked silicone adhesive sheetcan be carried out by first affixing the adhesive silicone sheet to thesemiconductor chip 1 and then affixing the semiconductor chip 1 to thesemiconductor chip support 3 via the aforementioned sheet, or by firstaffixing the adhesive sheet made of silicone to the semiconductor chipsupport 3 and then affixing the semiconductor chip 1 to thesemiconductor chip support 3 via the adhesive sheet. Although there areno special restrictions with regard to the temperature at which thecross-linked silicone adhesive sheet can be adhered to the semiconductorchip and the chip support, it is recommended to do this at a temperaturebetween 50° C. and 200° C., preferably between 100° C. and 150° C.Normally, in connecting the cross-linked silicone adhesive sheet 2 tothe semiconductor chip 1 and the chip support 3, heating is carried outin two steps. More specifically, after preliminary attachment withheating and application of pressure for 1 to 2 seconds, a post-curing iscarried out in an oven at 150° C. to 170° C. for final connection.

[0043] After curing, the semiconductor chip 1 and interconnects 4 areelectrically connected by bonding wires 5. Nornally, this is done byultrasonic welding. If necessary, the semiconductor chip 1 then can besealed with a resin sealant 6. Since a semiconductor chip can beattached to the chip support with the use of the silicone adhesive sheetat a relatively low temperature, there will be no danger of damaging thesemiconductor chip under the effect of heat. This, in turn, makes itpossible to improve reliability of the semiconductor device.

EXAMPLES

[0044] The cross-linked silicone adhesive sheet of the invention andmethod of manufacturing of this adhesive sheet will now be described indetail with reference to practical examples. The viscosity valuesreported in the examples were measured at 25° C. The following methodswere used to evaluate reliability and to measure the force required forpeeling a protective film from the cross-linked silicone adhesive sheet.

Force For Peeling a Protective Film from a Cross-linked SiliconeAdhesive Sheet

[0045] Test specimens were produced by cutting a cross-linked siliconeadhesive sheet with protective films adhered to both sides of the sheetinto 1 centimeter (cm)×15 cm strips. A protective film adhered to oneside of the test specimen (hereafter referred to as side A) was pulledaway from the specimen surface at an angle of 180° at a rate of 100millimeters per minute (mm/min). An average value of stress developedduring this action was measured. This average value was assumed as aforce of peeling of the protective film from the cross-linked siliconeadhesive sheet. The peeling force of the protective film from the otherside of the specimen (hereafter referred to as side B) was determined inthe same manner.

Manufacturing of a Semiconductor Device and Evaluation of InitialAdhesiveness

[0046] The cross-linked silicone adhesive sheet was used formanufacturing a semiconductor device shown in FIG. 1. More specifically,a semiconductor chip (1 cm×1 cm) and a semiconductor chip support (3cm×3 cm) made of polyimide were interconnected via the cross-linkedsilicone adhesive sheet (1 cm×1 cm), and then under a pressure developedby application of a 1 megaPascal (MPa) force, the unit was heated for 2seconds at 190° C. The pressure was released, and the obtained unit wasplaced into a 170° C. oven for 1 hour. The unit was then removed fromthe oven, and the polyimide-made semiconductor chip support and thecross-linked silicone adhesive sheet were visually observed. After thetest piece was formed from well adhered components, the bonding padslocated on the top of the semiconductor chip 1 and the interconnects 4were then electrically connected by wires 5 fixed with ultrasonicwelding.

Evaluation of Rejection Rate of Semiconductor Devices

[0047] The semiconductor device was inserted into a socket and wastested by passing electric current between the device terminals. In thecurrent test, the percentage of semiconductor devices that failed topass the current was considered as a rejection rate.

Practical Example 1

[0048] A Ross mixer was filled with the following components: 31 partsby weight of a 2,200 milli-Pascal seconds (mPa•s) viscositydimethylpolysiloxane having both molecular terminals capped withdimethylvinylsiloxy groups (with 0.23 wt. % content of vinyl groups) andcontaining 0.01 wt. % of a low-molecular-weight siloxane with vaporpressure exceeding 10 millimeters of mercury (mmHg) at 200° C.; 56 partsby weight of a 7,000 mPa•s viscosity organopolysiloxane mixture composedof 65 wt % of a 2,000 mPa.s viscosity dimethylpolysiloxane having bothmolecular terminals capped with dimethylvinylsiloxy groups (with 0.23wt. % content of vinyl groups) and 35 wt. % of an organopolysiloxaneresin composed of (CH₂═CH)(CH₃)₂SiO_(1/2) units, (CH₃)₃SiO_(1/2) units,and SiO_(4/2) units (with 2.5 wt. % content of vinyl groups); and 13parts by weight of fumed silica having BET specific surface area of 200m²/g. After mixing 1 hour at room temperature, the mixture was mixed foranother 2 hours at 170° C. under a reduced pressure. As a result, aftercooling the mixture to room temperature, a paste-like semitransparentsilicone rubber base was obtained.

[0049] 100 parts by weight of the obtained base were uniformly mixed invacuum with 6 parts by weight of a 5 mPa•s viscositydimethylsiloxane-methylhydrogensiloxane compolymer having both molecularterminals capped with trimethylsiloxy groups (with 0.73 wt. % content ofsilicon-bonded hydrogen atoms) and expressed by the following averagemolecular formula:

[0050] so that 1.8 moles of silicon-bonded hydrogen atoms of thiscomponent were used for 1 mole of vinyl groups in component (A), 1 partsby weight of an organopolysiloxane (with 16 wt. % content of vinylgroups) expressed by the following average-unit formula:

[0051] 0.5 parts by weight of a silatrane derivative expressed by thefollowing formula:

[0052] and a complex of platinum with 1,3-divinyltetramethyidisiloxane(with concentration of platinum metal in the complex equal to 5 ppm). Asa result, a 70,000 mPa•s viscosity silicone-rubber compositioncross-linkable via a hydrosilylation reaction was prepared. The totalcontent of uranium and thorium in the obtained composition did notexceed 0.1 ppb, and the total content of ions of sodium, potassium, orother alkali metal did not exceed 0.1 ppm.

[0053] The obtained silicone composition was sandwiched between a 50 μmthick surface-nontreated PES film and a 50 μm thick PES film having thesurface pretreated with Treatment Agent No. 1, a 30 mPa•s viscositymethylhydrogenpolysiloxane having both molecular terminals capped withtrimethylsiloxy groups (1.6 wt. % content of silicon-bonded hydrogenatoms). The obtained sandwich was rolled between a two-roll device withan adjustable clearance between the stainless-steel rolls so that thethickness of the silicone composition was 30 μm. A silicone-rubberadhesive sheet with PES films on both surfaces was produced afterheating the rolled sandwich for 30 minutes in an 80° C. oven withcirculation of hot air.

[0054] First, the PES film having the surface coated with TreatmentAgent No. 1 was stably peeled away from the obtained silicone rubberadhesive sheet. Measurement of forces required for peeling off bothprotective films showed that the PES film having the surface treatedwith Treatment Agent No. 1 could be peeled off with the peeling force of1.9 N/m, while the non-treated PES film could be peeled off with thepeeling force of 2.3 N/m.

[0055] A semiconductor device was produced by interconnecting asemiconductor chip and a chip support member by means of theaforementioned silicone rubber adhesive sheet. Adhesiveness of thesilicone rubber adhesive sheet to the semiconductor chip and to the chipsupport member was evaluated, and the rejection rate of semiconductordevices was determined. The results are shown in Table 1.

Practical Example 2

[0056] The silicone rubber composition cross-linkable via ahydrosilylation reaction and produced in Practical Example 1 wassandwiched between a 50 μm thick surface-nontreated PES film and a 50 μmthick PES film having the surface pretreated with Treatment Agent No. 2,a 10 mPa•s viscosity dimethylpolysiloxane having both molecularterminals capped with dimethyihydrogensiloxy groups (0.16 wt. % contentof silicon-bonded hydrogen atoms). The obtained sandwich was rolledbetween a two-roll device with an adjustable clearance between thestainless-steel rolls so that the thickness of the silicone compositionwas 30 μm. A silicone-rubber adhesive sheet with PES films on bothsurfaces was produced after heating the rolled sandwich for 30 min. inan 80° C. oven with circulation of hot air.

[0057] First, the PES film having the surface not treated with TreatmentAgent No. 2 was stably peeled away from the obtained silicone rubberadhesive sheet. Measurement of forces required for peeling off bothprotective films showed that the PES film having the surface treatedwith Treatment Agent No. 2 could be peeled off with the peeling force of2.8 N/m, while the non-treated PES film could be peeled off with thepeeling force of 2.3 N/m.

[0058] A semiconductor device was produced by interconnecting asemiconductor chip and a chip support member by means of theaforementioned silicone rubber adhesive sheet. Adhesiveness of thesilicone rubber adhesive sheet to the semiconductor chip and to the chipsupport member was evaluated, and the rejection rate of semiconductordevices was determined. The results are shown in Table 1.

Practical Example 3

[0059] The silicone rubber composition cross-linkable via ahydrosilylation reaction and produced in Practical Example 1 wassandwiched between a 50 μm thick surface-nontreated PES film and a 50 μmthick surface-nontreated TAC film. The obtained sandwich was rolledbetween a two-roll device with an adjustable clearance between thestainless-steel rolls so that the thickness of the silicone compositionwas 30 μm. A silicone-rubber adhesive sheet having a PES film adhered toone side and a TAC film adhered to the other side was produced afterheating the rolled sandwich for 30 min. in an 80° C. oven withcirculation of hot air.

[0060] First, the TAC film was stably peeled away from the obtainedsilicone rubber adhesive sheet. Measurement of forces required forpeeling off both protective films showed that the surface-nontreated TACfilm could be peeled off with the peeling force of 0.7 N/m, while thesurface nontreated PES film could be peeled off with the peeling forceof 2.3 N/m.

[0061] A semiconductor device was produced by interconnecting asemiconductor chip and a chip support member by means of theaforementioned silicone rubber adhesive sheet. Adhesiveness of thesilicone rubber adhesive sheet to the semiconductor chip and to the chipsupport member was evaluated, and the rejection rate of semiconductordevices was determined. The results are shown in Table 1.

Practical Example 4

[0062] The silicone rubber composition cross-linkable via ahydrosilylation reaction and produced in Practical Example 1 wassandwiched between a 50 μm thick surface-nontreated PES film and a 50 μmthick PET film having a 1 μm thick TAC film adhered to the surface ofthe composition. The obtained sandwich was rolled between a two-rolldevice with an adjustable clearance between the stainless-steel rolls sothat the thickness of the silicone composition was 30 μm. Asilicone-rubber adhesive sheet having a PES film adhered to one side anda TAC-PET film adhered to the other side was produced after heating therolled sandwich for 30 minutes in an 80° C. oven with circulation of hotair.

[0063] First, the TAC-PET film was stably peeled away from the obtainedsilicone rubber adhesive sheet. Measurement of forces required forpeeling off both protective films showed that the TAC-PET film could bepeeled off with the peeling force of 0.7 N/m, while the surfacenontreated PES film could be peeled off with the peeling force of 2.3N/m.

[0064] A semiconductor device was produced by interconnecting asemiconductor chip and a chip support member by means of theaforementioned silicone rubber adhesive sheet. Adhesiveness of thesilicone rubber adhesive sheet to the semiconductor chip and to the chipsupport member was evaluated, and the rejection rate of semiconductordevices was determined. The results are shown in Table 1.

Practical Example 5

[0065] The silicone rubber composition cross-linkable via ahydrosilylation reaction and produced in Practical Example 1 wassandwiched between a 50 μm thick PET film having a 2 μm thick PES layeron the surface and a 50 μm thick PET film having a 1 μm thick TAC layeron the surface adhered to the surface of the composition. The obtainedsandwich was rolled between a two-roll device with an adjustableclearance between the stainless-steel rolls so that the thickness of thesilicone composition was 30 μm. A silicone-rubber adhesive sheet havinga PES-PET film adhered to one side and a TAC-PET film adhered to theother side was produced after heating the rolled sandwich for 30 minutesin an 80° C. oven with circulation of hot air.

[0066] First, the TAC-PET film was stably peeled away from the obtainedsilicone rubber adhesive sheet. Measurement of forces required forpeeling off both protective films showed that the TAC-PET film could bepeeled off with the peeling force of 0.7 N/m, while the surfacenontreated PES-PET film could be peeled off with the peeling force of2.3 N/m.

[0067] A semiconductor device was produced by interconnecting asemiconductor chip and a chip support member by means of theaforementioned silicone rubber adhesive sheet. Adhesiveness of thesilicone rubber adhesive sheet to the semiconductor chip and to the chipsupport member was evaluated, and the rejection rate of semiconductordevices was determined. The results are shown in Table 1.

Comparative Example 2

[0068] The silicone rubber composition cross-linkable via ahydrosilylation reaction and produced in Practical Example 1 wassandwiched between a 50 μm thick surface-nontreated PES film and another50 μm thick surface-nontreated PES film. The obtained sandwich wasrolled between a two-roll device with an adjustable clearance betweenthe stainless-steel rolls so that the thickness of the siliconecomposition was 30 μm. A silicone-rubber adhesive sheet having a PESfilm adhered to both sides of the sheet was produced after heating therolled sandwich for 30 minutes in an 80° C. oven with circulation of hotair.

[0069] When the PES film was peeled away from one side of the obtainedsilicone rubber adhesive sheet, the peeling surface was unstable andpartial peeling of the PES film on the opposite side of the sheet wasobserved. Measurement of forces required for peeling off both nontreatedprotective films showed the peeling force of 2.3 N/m.

Comparative Example 2

[0070] The silicone rubber composition cross-linkable via ahydrosilylation reaction and produced in Practical Example 1 wassandwiched between a 50 μm thick surface-nontreated PET film and another50 μm thick surface-nontreated PET film. The obtained sandwich wasrolled between a two-roll device with an adjustable clearance betweenthe stainless-steel rolls so that the thickness of the siliconecomposition was 30 μm. A silicone-rubber adhesive sheet having a PESfilm adhered to both sides of the sheet was produced after heating therolled sandwich for 30 minutes in an 80° C. oven with circulation of hotair.

[0071] When the PET film was peeled away from one side of the obtainedsilicone rubber adhesive sheet, the peeling surface was unstable andpartial peeling of the PET film on the opposite side of the sheet wasobserved. Measurement of forces required for peeling off bothnon-treated protective films showed the peeling force of 10 N/m, peelingwas extremely difficult, and the films had low peelability. TABLE 1 Pr.Ex. Pr. Ex. Pr. Pr. Ex. Pr. Ex. Comp. Comp. 1 2 Ex. 3 4 5 Ex. 1 Ex. 2Side A PES PES PES PES PET PES PET protective film film film film filmfilm film film with PES layer on the surface Side B PES PES TAC PET PETPES PET protective film film film film film film film film treatedtreated with with with with TAC TAC Agent Agent layer layer No. 1 No. 2on the on the surface surface First peeled side B A B B B A A Stabilityof Stable Unstable peeling surface Peeling force on 2.3 2.3 2.3 2.3 2.32.3 10 side A (N/m) Peeling force on 1.9 2.8 0.7 0.7 0.7 2.3 10 side B(N/m) Adhesiveness Good Good Good Good Good — — Rejection rate 0/30 0/300/30 0/30 0/30 — —

INDUSTRIAL APPLICABILITY

[0072] In peeling away protective films from both sides of thecross-linked silicone adhesive sheet of the invention, both peelingsurfaces show stability. Furthermore, the aforementioned cross-linkedsilicone adhesive sheet can be efficiently produced by the method of thepresent invention for manufacturing cross-linked silicone adhesivesheets. Therefore, the cross-linked silicone adhesive sheet of theinvention is used for attaching a semiconductor chip to a chip support.

What is claimed is:
 1. An adhesive sheet characterized by: (A) across-linked silicone with a thickness of 100 μm or less, (B) a firstprotective film on one side of the cross-linked silicone, and (C) asecond protective film on the opposite side of the crosss-linkedsilicone, where a peeling force of component (B) away from said adhesivesheet is equal to or below 5.0 N/m, where a peeling force of component(C) away from said adhesive sheet is equal to or below 5.0 N/m, andwhere the difference between peeling forces of component (B) andcomponent (C) is equal to or exceeds 0.2 N/m.
 2. The adhesive sheet ofclaim 1, characterized in that component (A) comprises a product ofcross-linking a silicone composition selected from a group ofcrosslinkable silicone compositions consisting essentially of (i)cross-linkable by a hydrosilylation reaction, (ii) cross-linkable by acondensation reaction, (iii) cross-linkable by a radical cross-linkingreaction with the use of an organic peroxide, and (iv) cross-linkablewith the use of ultraviolet rays.
 3. The adhesive sheet of claim 1characterized in that component (A) comprises a product of cross-linkinga silicone composition cross-linkable by a hydrosilylation reaction. 4.The adhesive sheet of claim 3, characterized in that said siliconecomposition is cross-linkable by a hydrosilylation reaction comprising:(A) an organopolysiloxane having at least two alkenyl groups permolecule, (B) an organopolysiloxane having at least two silicon-bondedhydrogen atoms per molecule, (C) adhesion accelerator, and (D) a metalhydrosilylation catalyst.
 5. The adhesive sheet of claim 1 characterizedin that component (B) and component (C) are made of different materials.6. A method of manufacturing the adhesive sheet of claim 5 characterizedby: (1) forming a film-like body by placing (A) the cross-linkablesilicone composition in a layer having a thickness of 100 μm or lessbetween (B) the first protective film and (C) the second protectivefilm, and (2) cross-linking component (A).
 7. A method of manufacturingan adhesive sheet characterized by: (1) pretreating either (B) a firstprotective film or (C) a second protective film with anorganopolysiloxane having at least two silicon-bonded hydrogen atoms permolecule, (2) forming a film-like body by placing (A) a cross-linkablesilicone composition in a layer having a thickness of 100 μm or lessbetween component (B) and component (C) so as to contact component (A)with the organopolysiloxane on the surface of either component (B) orcomponent (C), and (3) cross-linking component (A); wherein a peelingforce of component (B) away from the product of step (3) is equal to orbelow 5.0 N/m, wherein a peeling force of component (C) away from theproduct of step (3) is equal to or below 5.0 N/m, and wherein thedifference between peeling forces of component (B) and component (C) isequal to or exceeds 0.2 N/m.
 8. An adhesive sheet prepared by the methodof claim
 7. 9. A device characterized by: (a) a semiconductor chip, (b)a semiconductor chip support, and (c) an adhesive sheet according toclaim 1, wherein the semiconductor chip and the semiconductor chipsupport are bonded together by the adhesive sheet.
 10. The device ofclaim 9, characterized in that the device comprises a diode, atransistor, a thyristor, and a circuit selected from the groupconsisting of (i) a monolithic integrated circuit, (ii) a hybridintegrated circuit, (iii) a large-scale integrated circuit, and, (iv) avery large-scale integrated circuit.